Inorganic binder composition and refractory-binder coated fabric compositions prepared therefrom

ABSTRACT

An inorganic binder usefully employed in providing refractory coatings on fabric substrates is prepared from colloidal silica, monoaluminum phosphate, aluminum chlorohydrate and a catalyst of an alkyl tin halide.

This is a divisional of co-pending application Ser. No. 585,909 filedMar. 2, 1984, now U.S. Pat. No. 4,507,355.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to refractory-binder coated compositions. Moreparticularly, it relates to an inorganic binder composition which mayusefully be employed, in combination with refractory materials, inpreparing refractory-binder coated compositions. This invention isespecially related to refractory-binder compositions which may beapplied to woven, knitted or non-woven fabrics constructed from textileyarns to provide them with high temperature resistance and flameresistance.

2. Description of the Prior Art

Ceramics and/or glass fibers have been used herebefore to prepare hightemperature electrical insulating tape. U.S. Pat. No. 4,358,500discloses refractory coated insulating compositions wherein therefractory coating, comprising refractory materials and an inorganicbonding agent, is formed on the surface and, necessarily, theinterstices of a porous base fabric, such as a knitted fiberglassfabric. In the presence of extreme temperatures and heat, the refractorymaterials fuse into the softened surface of the base fabric, enabling itto withstand intense heat, flame impingement, flame abrasion, andelevated temperatures well beyond the normal temperature limitations ofthe fabric. The resulting fabric structure will have ceramic qualitiesand will not soften, melt, drip or lose its insulating properties.

Commonly assigned patent application Ser. No. 338,850, now U.S. Pat. No.4,428,999 and U.S. Pat. Nos. 4,375,493 and 4,396,661 relate tomulti-functional fabric compositions having a refractory coating on oneside of the base fabric and a different coating providing a differentfunction on the other side, i.e., the '850 application--a vapor barriercoating, the '493 patent--a conductive coating and the '661 patent--adielectric coating.

The inorganic bonding agent disclosed in U.S. Pat. No. 4,358,500 isprepared from colloidal silica, monoaluminum phosphate (MAP) andaluminum chlorohydrate (ACH) by adding the MAP and ACH separately to thecolloidal silica which acts as a liquid moderator. Although thecompositions containing the inorganic bonding agent of U.S. Pat. No.4,358,500 may be exposed to high temperatures, no products of combustionin the form of smoke or fumes are produced as with other prior artcoated fabrics. Further, the refractory coated compositions preparedwith the inorganic bonding agent proved superior to inorganic coatingsavailable for use on fabrics or paper substrates. The latter inorganiccoatings could be damaged by water. They could be wet by water and thewater could solvate the coating to the point of causing the inorganiccoating to dissociate itself from the substrate. Although other binders,such as the acrylics, inhibited this wetting action, they would burn offwhen subjected to flame and high temperature. The refractory coatedsubstrates disclosed in the '500 patent, on the other hand, are notwetted by water and are not subject to the solvation action of water asare other inorganic coatings. However, despite these advantages, therefractory coated compositions of the '500 patent exhibit a veryundesirable feature. This refractory coating must be applied to a porousfabric so that the coating will be placed in the interstices of thefabric. This is necessary to achieve the formation of the refractorycoating on this fabric. However, this requires the use of a largerquantity of the refractory coating when preparing these compositions tothe extent that the coating in many instances constitutes about 50% ofthe overall weight of the impregnated base fabric. The result of allthis is that when this coated fabric is flexed, the bond of therefractory coating to the substrate is disrupted and some particles maybe released to the surface resulting in "dusting" of the coating. This,of course, is highly undesirable despite the very desirable features offlame and high temperature resistance which are exhibited by theserefractory coated compositions.

It is an object of this invention to provide an improved inorganicbonding agent (binder) which may be usefully employed in preparingrefractory-binder coated compositions and which will provide an intimatebond between the refractory coating and the fibrous surface of the yarncomprising the fabric so that the coating will not dissociate itselffrom the fiber upon flexure of the coated composition.

It is another object of this invention to provide refractory coatedfabric compositions which will not exhibit "dusting" of the refractorycoating in use.

SUMMARY OF THE INVENTION

These and other objects of this invention have been achieved bypreparing an inorganic bonding agent from colloidal silica, monoaluminumphosphate, aluminum chlorohydrate and an organic tin halide catalyst.This bonding agent is combined with refractory material and applied tobase fabrics to provide refractory-binder coated compositions which donot "dust" as heretofore and which have flame and high temperatureresistance. This inorganic binder composition is an improvement over thebonding agent disclosed in U.S. Pat. No. 4,358,500 and leads to the useof substantially lower coating weights while providing the same watershedding properties and the same flame and fire protection as therefractory coated compositions disclosed therein. Further, thesignificantly improved bonding does not require that the coating has tobe placed in the interstices of the fabric and, hence, the base fabricsemployed herein need not be porous.

The present invention relates to an inorganic binder compositioncomprising:

(a) colloidal silica;

(b) monoaluminum phosphate;

(c) aluminum chlorohydrate; and

(d) an amount of an alkyl tin halide catalyst effective to increase thebonding of said composition when applied to a substrate.

In a preferred embodiment, the present invention relates to a heatresistant, refractory coated composition comprising:

(a) a base fabric, and

(b) a refractory coating comprising refractory materials and the aboveinorganic binder composition, said refractory coating bonded to thesurface of the fabric and said refractory materials being capable ofproviding flame abrasion resistance and heat resistance to the basefabric at elevated temperatures.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is an improvement of the heat resistant,refractory, insulating fabric compositions of U.S. Pat. No. 4,358,500,the entire contents of which are incorporated herein by reference. Theterms binder and bonding agent are used interchangeably herein todescribe compositions having the same utility. Thus, the inorganiccomposition of U.S. Pat. No. 4,358,500 is described therein as a bondingagent while the inorganic composition of the present invention which isan improvement of the bonding agent of U.S. Pat. No. 4,358,500 isdescribed herein as a binder. Both compositions, when combined withrefractory materials and applied to an acceptable substrate, will "bond"or "bind" these materials to the substrate, although not to the samedegree.

Briefly, the inorganic binder of the present invention comprises thethree components of the prior art bonding agent to which is added acatalyst which promotes the curing of the binder when it is applied toan appropriate surface and increases the bond between this surface andthe binder composition. The preferred catalyst is an organometallichalide, specifically, a lower alkyl tin halide. The alkyl tin halidecatalyst is preferably a trialkyl tin chloride, most preferably, atri-butyl tin chloride and especially, triisobutyl tin chloride. Aparticularly preferred catalyst which may be employed in the binder ofthis invention is a product of Dow Corning Corporation, Midland, Mich.known as Dow Corning catalyst 182A, wherein the active ingredient istriisobutyl tin chloride.

When practicing this invention the refractory coating which is appliedto the appropriate fabric substrate comprises heat resistant refractorymaterials intermixed or dispersed in the binder. The refractorymaterials may be any of the usual known refractory materials in finelydivided form and include compounds of aluminum, calcium, chromium,magnesium, silicon, titanium, zirconium and the like, such as aluminumoxide, calcium oxide, magnesium oxide, silicon oxide, titanium oxide,zirconium oxide, aluminum silicate, calcium silicate, magnesiumsilicate, silcon carbide, zirconium carbide and the like. Alumina,zirconia, calcium silicate and silicon dioxide are preferred, alone orin combination. These materials enable the compositions of thisinvention to maintain their heat insulating ability after prolongedexposure to temperatures in the 2200° F. range.

In addition to these ceramic-type materials, other useful refractorymaterials may be employed to provide compositions which may be employedat temperatures in the 3000° F. plus range. These refractory materialsinclude, for example, zirconium oxide, silicon carbide, alumina-silicafiber, carbon fiber, zirconia fiber, graphite and thermal carbon black.This later material is a non-electrical conducting form of carbon blackwhich is resistant to temperatures as high as 7000° F.

The all inorganic composition of this invention is employed as thebinder composition, i.e., the bonding agent for the refractory materialsin the refractory coating. The refractory coating is applied to the basefabric and then subjected to a source of heat to remove water from thecoating and to initiate the catalytic action which causes an increasedbonding of the refractory material to the surface of the fabric. Thisprovides the fabric composition with a coating which will permit use athigh temperatures and will resist direct flame abrasion and will notdust.

The inorganic composition of this invention is liquid and is formed fromcolloidal silica, the catalyst, monoaluminum phosphate and aluminumchlorohydrate. The later two materials cannot normally be employed incombination since when they are combined the result is highlyexothermic, producing a pliable mass which develops into a solidmaterial. By employing the colloidal silica, which acts as a liquidmoderator, the monoaluminum phosphate (MAP) and the aluminumchlorohydrate (ACH) may be used in combination to achieve the desiredresults. The catalyst further promotes the reaction and achieves animproved bonding between the binder and the fabric substrate.

In formulating the inorganic composition employed in this invention, thequantities of the components may be varied over a considerable range. Itis usually convenient to provide the monoaluminum phosphate and thealuminum chlorohydrate in a weight ratio of MAP to ACH of about 0.8:1.0to about 1.5:1.0, preferably about 1.0:1.0 to about 1.25:1.0. Thequantity of colloidal silica to be employed is based on the weight ratioof the liquid colloidal silica to the combined weights of the MAP andthe ACH. A weight ratio range of colloidal silica to MAP plus ACH ofabout 0.6:1 to about 1:1, preferably about 0.75:1 to 0.85:1 has beenfound useful. The quantity of catalyst to be employed is based on theweight ratio of the liquid catalyst to the combined weights of the MAP,the ACH and the colloidal silica. A weight ratio range of catalyst toMAP, ACH and colloidal silica of about 0.025:1.0 to about 0.125:1.0,preferably about 0.06:1 to about 0.08:1.0 has been found useful.Preferably, the binder composition should be applied as a coating in adilute concentration by adding a quantity of water to the combinedingredients. A ratio of the combination of MAP, ACH and colloidal silicato water of about 0.5:1.0 to about 1.0:1.0 can be effective employed.The water employed should be soft or at least deionized to achieve bestresults. Additional water may be used as a diluent in various coatingtechniques without deleterious effects.

Since the catalyst promotes the reaction of the components, the bindercomposition has a definite pot time, usually about 2 to about 3 or morehours. In general, the more water added to the mixture, the longer thepot time.

In preparing this inorganic binder, the required amounts of MAP and ACHare separately added to the colloidal silica. The catalyst, therefractory materials and the necessary amount of water are added tocomplete the formulation of the refractory coating. This coating may beapplied to the fabric substrate and maintained at an elevatedtemperature for a period of time sufficient to cause removal of thewater and permit the MAP and the ACH, in the presence of the catalyst,to react slowly producing a slowly thickening material which bonds therefractory materials to the surface of the fabric substrate andproviding a unitary structure having flame and high temperatureresistant properties and an inorganic coating which is not watersoluble.

When the refractory coating has been bonded to the fabric substrate, theresulting coating has an acid pH which should be neutralized or thechemical bonding action will continue slowly over a period of timecausing the underlying fabric to lose some degree of flexibility. Thisacidity may be neutralized by a dilute alkali solution of ammonia,caustic and the like. The solution may be sprayed onto the coated fabricor the fabric may be passed through a bath of the dilute alkalisolution. Following the neutralization, the coated fabric can be airdried or slowly dried in streams of warm air. Where loss of fabricflexibility creates no particular problem, the neutralization step canbe eliminated.

The surface of the refractory coated fabric composition prepared inaccordance with this invention may appear to be slightly abrasive,principaly because of the presence of refractory materials, even thoughthey are in finely divided form. To remove this abrasiveness and toimprove the flexibility and the "hand" of the coated fabric, a siliconeelastomer coating may be applied to the refractory coating. A coating ofa silicone elastomer can be formed on the coated fabric by applying aone-component, water based emulsion of a silicone elastomer, such as aproduct known as Dow Corning Q3-5025. This one-component siliconematerial is cured by simple evaporation of water at room temperature.The evaporation of water may be accelerated at elevated temperatures.The water based silicone elastomer emulsion provides a desirable sideeffect since it neutralizes the acid pH of the refractory coating. Thus,when a silicone rubber coating is applied to the compositions of thisinvention, there is no need to employ the dilute alkali neutralizationdescribed above. The resulting silicone rubber coated fabric is smoothto the touch and is easily handled. The silicone coating provides a veryflexible product since not only does it stop the catalyzed reaction andthe further hardening of the coating, but it lubricates the surfaces ofthe refractory coated fabric so that these surfaces can rub togetherwith less friction and add flexibility to the fabric composition.

The refractory coating prepared in accordance with this invention may beapplied to a wide variety of fabric substrates and will achieve a goodbond even if the fabric has a smooth surface. The binder may be employedas the only binder in the resulting composition or it may be combinedwith any known binder conventionally employed with the subject substrateto provide the resulting composition with flame and heat resistantproperties. Those skilled in the art will appreciate that the dissimilarbinder which is combined with the refractory coating which contains thebinder of this invention must be compatible with the latter binder. Thatis, the combination of binders must not produce any undesirable sideeffects or reactions.

The base fabrics which form the substrate for the compositions of thisembodiment may be composed of a wide range of materials includingnatural or synthetic materials or mixtures thereof. Thus, fabricscontaining such natural materials as cotton, silk, wool, and the likeand such man-made and polymeric materials as glass, mineral wool, nylon,dacron, aramid, and the like, alone or in combination may be employed.

Although the refractory coating containing the inorganic binder of thisinvention will provide high temperature properties to the base fabric,it will not render combustible material in the fabric non-combustible.However, any non-combustible fabric or any combustible fabric which canbe rendered fireproof will have its flame resistance increased to ahigher threshold when the refractory coating prepared in accordance withthis invention is applied to such fabric. Phosphate treatment ofcellulosic material and similar treatments known in the art for othercombustible materials will render these materials flameproof.

As used herein, the term "fabric" includes materials which are woven,knitted or non-woven. Non-woven fabrics herein include an assembly oftextile fibers held together by mechanical interlocking in a web or matby such procedures as needle punching, by fusing of the fibers or bybonding with a cementing medium. In most instances, the "fabrics"employed herein will be constructed from interlocking yarns, fibers orfilaments.

The base fabric employed in the prior art refractory coated compositionshad to have a porosity, i.e., there had to be an openness to the textureof the fabric so as to permit the refractory coating to impregnate thesurface of the fabric and fill, at least partially, some, if not all, ofthe interstices of the porous fabric. In contradistinction, the fabricsemployed in the present invention need not have the porosity which isrequired in the prior art when preparing refractory coated fabrics. Therefractory coating prepared with the inorganic binder of this inventionwill bond to the surface of the fabric wherever exposed and it will evenbond to a fabric having a smooth, as opposed to an irregular, surface.There is no need in the present invention for the refractory coating tobe located in the interstices of a fabric to achieve a coating of thefabric as is required when preparing refractory coated compositions suchas those of U.S. Pat. No. 4,358,500.

A fabric preferred in this invention is one composed of fiberglass. Thissubstrate may be woven fiberglass, knitted fiberglass or a non-woven webof fiberglass.

As will be understood by those skilled in the art, a fiberglasssubstrate fabric, though it may be formed of all fiberglass yarns, mayalso be constructed of combinations of fiberglass yarn with other fireresistant yarns.

The following serves to illustrate the subject invention. An inorganiccomposition usefully employed in this invention contains the followingingredients, listed in their order of addition:

                  TABLE I                                                         ______________________________________                                                            Parts (By Weight)                                         ______________________________________                                        Water                 16                                                      Colloidal Silica (Nyacol 2034 DI)                                                                   30                                                      (34% Solids)                                                                  Monoaluminum Phosphate (MAP)                                                                        20                                                      (42% Solids)                                                                  Aluminum Chlorohydrate (Cawoods-5025)                                                               20                                                      (32% solids)                                                                  Catalyst (Dow Corning catalyst 182A)                                                                 5                                                      (21% solids)                                                                  Water                 48                                                      ______________________________________                                    

The liquid inorganic composition is formed by slow addition of MAP tothe mixture of water and colloidal silica while mixing, followed by theslow addition of the ACH while mixing. Mixing should be continued whilethe catalyst is added and is continued until a slight increase inviscosity occurs and a smooth consistency is achieved. The colloidalsilica and the water acts as a moderator to delay the rapid exothermalchemical reaction that would normally occur when MAP is mixed with ACH.Although the rapid chemical reaction between the MAP and ACH is greatlyslowed by the colloidal silica and water moderator, a partial reactiondoes occur which is the cause of the initial viscosity increase when ACHis added to the mixture. After the catalytic action starts, the finaladdition of water is made. The catalyst further promotes the reactionwhich causes the binder, together with the refractory materials, tobecome bound to the substrate to which it has been applied.

The refractory coating of this invention can be formed as a thin coatingon the base fabric. This is in contrast to the refractory coated fabriccompositions of U.S. Pat. No. 4,358,500 where the coating constitutedabout 50% of the overall weight of the coated fabric. In the coatedfabrics of the present invention, the refractory coating may constituteas little as 10 to 20% of the total weight of the coated fabric. It isthe increased bonding achieved with the present inorganic binder whichmakes this possible.

A high temperature refractory coating may be formed by adding hightemperature refractory materials to the liquid inorganic composition andmixing to a smooth consistency. Refractory materials, alone or incombination, for example, zirconium oxide, alumina-silica fiber, carbonfiber, zirconia fiber, graphite or thermal carbon black and the like,may be employed. One particularly preferred refractory coating comprisesthe above binder plus refractory materials of alumina-silica fiber andzirconium oxide. In forming this coating, the refractory materials arepreferably added after the MAP but before the ACH. This preferredrefractory coating has the composition set forth in Table II where theingredients are listed in the order of their addition. As prepared, thiscoating has a solids composition of 30.7%.

                  TABLE II                                                        ______________________________________                                                            Parts (By Weight)                                         ______________________________________                                        Water                 16                                                      Colloidal Silica (Nyacol 2034 DI)                                                                   30                                                      (34% Solids)                                                                  Monoaluminum Phosphate (MAP)                                                                        20                                                      (42% Solids)                                                                  Alumina Silica Fiber (Fiberfax)                                                                     24                                                      Zirconium Oxide (Tam Zirox 250)                                                                      8                                                      Aluminum Chlorohydrate (Cawoods-5025)                                                               20                                                      (32% solids)                                                                  Catalyst (Dow Corning catalyst 182A)                                                                 5                                                      (21% solids)                                                                  Water                 48                                                      ______________________________________                                    

The binder composition employed in this invention may be employed aloneas a single bonding agent or binder or, alternatively, the binder may beemployed in combination with any of the commercial binders, oftenorganic, that are conventionally employed in preparing certain fabriccompositions. The relative amounts of conventional, i.e., dissimilar,binder and the inorganic binder composition of this invention will bedependent on factors, inter alia, such as compatibility of the twobinders, and the mechanical integrity required for the service in whichthe fabric composition product will be placed.

Curing the inorganic composition, after it is applied to the porous basefabric as part of the refractory coating may be achieved by any of anumber of procedures. Fabric temperatures of about 250° F. are usuallyeffective, although lower or higher temperatures may be employed, whererequired. An infrared source of heat has been found effective. Equallyuseful is a stream of forced dry air. Passing the coated fabric througha drying oven in a continuous fashion is an effective drying techniquewhere the composition is being prepared in a continuous operation. Thewater is removed first and during the course of this, the curing isinitiated and is effected by the time the coating is dry.

The dried refractory coating may impart a stiffness to the finishedfabric composition. Where this stiffness is undesired, it is possible toretain flexibility of the fabric composition by neutralizing the pH ofthe coating with a dilute alkali solution or a water based emulsion of asilicone rubber as described above.

The practice of the subject invention is illustrated in the followingexample.

A refractory coated fiberglass fabric was prepared as follows:

The ingredients of the binder composition were those of Table I and therefractory material consisted of alumina-silica fiber. The refractorycoating had the composition shown in Table III, where the ingredientsare listed in their order of addition.

                  TABLE III                                                       ______________________________________                                                            Parts (By Weight)                                         ______________________________________                                        Water                 32                                                      Colloidal Silica (Nyacol 2034 DI)                                                                   60                                                      (34% Solids)                                                                  Monoaluminum Phosphate (MAP)                                                                        40                                                      (42% Solids)                                                                  Alumina Silica Fiber (Fiberfax)                                                                     48                                                      (Ball Milled)                                                                 Aluminum Chlorohydrate (Cawoods 5025)                                                               40                                                      (32% Solids)                                                                  Catalyst (Dow Corning catalyst 182A)                                                                10                                                      (21% Solids)                                                                  Water                 96                                                      TOTAL                 326                                                     ______________________________________                                    

This coating, which did not contain any zirconium oxide employed in thepreferred composition of Table III, has a lower heat resistance than thepreferred composition.

Water and colloidal silica were mixed together. While this mixture wascontinuously being mixed, the remaining ingredients were slowly addedthereto. Each ingredient was thoroughly mixed into the mixture beforethe next ingredient was added. After the final addition of water, themixing was continued until the inorganic mixture was homogenous andsmooth.

A piece of woven fiberglass cloth (DE-150-1/0 by DE-150-1/0) was placedin the bottom of a shallow flat bottom tray and the above liquidinorganic mixture was poured over the cloth. The mixture was worked intothe surface of the glass cloth until all surfaces were thoroughlywetted. The cloth was then placed on a flat surface and excessquantities of the mixture were removed with a doctor blade. The wettedcloth was then placed under a set of infrared lamps until the coatedcloth was dry. The product obtained had a refractory coating whichprovided a slightly roughed surface to the cloth and exhibited an acidpH.

A coating of a one-component water based silicone elastomer emulsion wasapplied to the surface of the cloth. This emulsion consisted of 40 partsof Dow Corning Water Based Silicone Elastomer Q3-5025 and 240 parts ofwater. The wetted cloth was again placed under the infrared lamps untilthe surface of the cloth was dry. The surface was now smooth and thecloth had improved flexibility and "hand".

A strip of the coated fiberglass and a strip of the uncoated fiberglasswere each suspended in a chamber. The flame of a propane torch was heldagainst each sample. A hole immediately appeared in the uncoatedfiberglass cloth. The refractory coated fiberglass, on the other hand,resisted the flame abrasion for 20-30 seconds. During this time, thesurface of the cloth became discolored indicating the removal of thesilicone elastomer. The fiberglass at the point of flame impact appearedto soften with the refractory materials melting into it. After thisoccurred, the refractory coating caused the fabric to harden with aceramic surface which was highly fire retardant and resisted flameabrasion for relatively long periods.

A strip of knitted fiberglass was coated with a refractory coatingsimilar to that of Table III except that it did not contain any of thecatalyst. After being dried, the strip of refractory coated knittedfiberglass composition was compared to a strip of the refractory coatedwoven fiberglass of the invention.

    ______________________________________                                                     Knitted   Woven                                                               Fiberglass                                                                              Fiberglass                                                          Composition                                                                             Composition                                                         (Prior Art)                                                                             (Invention)                                            ______________________________________                                        Coating weight, %                                                                            50          10                                                 of coated fabric                                                              Effect of repeated                                                                           Visible dusting                                                                           No visible                                         flexing        of surface  dusting of                                                                    surface                                            ______________________________________                                    

What is claimed is:
 1. An inorganic binder composition comprising:(a) colloidal silica; (b) monoaluminum phosphate; (c) aluminum chlorohydrate; and (d) an amount of an alkyl tin halide catalyst effective to increase the bonding of said composition when applied to a substrate.
 2. A composition according to claim 1 wherein the weight ratio of colloidal silica to monoaluminum phosphate plus aluminum chlorohydrate is about 0.6:1 to 1:1, the weight ratio of monoaluminum phosphate to aluminum chlorohydrate is about 0.8 to 1.0 to about 1.5 to 1.0 and the weight ratio of catalyst to the combined weight of the colloidal silica, the monoaluminum phosphate and the aluminum chlorohydrate is about 0.025 to 1.0 to about 0.125 to 1.0.
 3. A binder composition according to claim 1 wherein the alkyl tin halide catalyst is triisobutyl tin chloride.
 4. A binder composition comprising at least 10 wt. % of the composition of claim 1 and 90 wt. % or less of a dissimilar binder, said dissimilar binder being compatible with the composition of claim
 1. 5. A heat resistant refractory coating comprising refractory materials and the inorganic composition of claim
 1. 6. A refractory coating according to claim 5 wherein the refractory materials are alumina-silica fiber, carbon fiber, zirconia fiber, zirconium oxide or mixtures thereof. 